Orthopedic prosthetic knees usually comprise a tibial component and a femoral component. In some instances, an artificial patella may also be provided. The tibial component frequently has a metal baseplate which is adapted to be mounted on a resected proximal end of the tibia. The baseplate has various fixation means to attach it to the tibia as, for example, a central shaft extending into the medullar canal, pins, porous or textured areas for bone ingrowth, or bone screws. On the base is mounted an articulating surface, usually made of ultra high molecular weight polyethylene. This articulating surface forms two condyle compartments: a larger medial compartment and a somewhat smaller lateral compartment.
The femoral compartment of the knee prosthesis is mounted on the resected distal end of the femur. The component is usually all metal and presents artificial condyles, one medial and one lateral, which slidingly engage the articulating surface of the tibial component. The femoral component is also affixed to its bone by various means, including a medullar shaft, porous or textured surfaces, or pins. In particular, pins are frequently provided located behind each condyle and extending in a direction which corresponds to the major axis of the femur. These pins help to establish rotational stability of the component with respect to the femur.
The effectiveness of a knee prosthesis is dependent, among other things, on the degree to which the two implanted components implanted correspond with the anatomy of the particular patient. As the leg of a patient moves, the components of the knee prosthesis can be expected to articulate against one another and their interaction will be effected by the accuracy of implantation with respect to the patient's bone. Jigs and other surgical apparatus assist surgeons in accurately placing the components of the prosthesis. Jigs for providing holes or starting bores for the condyle pegs described above are known. It is also known, however, that human anatomy varies from patient to patient. The optimum orientation of the components and in particular the femoral component varies within what is usually a small and well defined range. It is desirable to provide a jig which can accommodate such variation from patient to patient. Some jigs of this kind are available. For example, Richards Medical Products has marketed a femoral component jig for the condylar pins having separate drill hole plates for a range of angular variation. There remains, however, need for continued improvement in surgical apparatus.